1. Field of the Invention
The present invention relates to a sheet processing apparatus that performs post-processing on sheets, and an image forming system including the sheet processing apparatus.
2. Description of the Related Art
Conventionally, there has been known a sheet processing apparatus that performs post-processing on sheets output from an image forming apparatus. Examples of this type of sheet processing apparatus include one that stacks sheets on a processing tray, aligns the sheets by pushing lateral edges thereof by alignment members, and then performs post-processing, such as stapling processing, on the sheets.
By the way, conventionally, there has been known an image forming apparatus that corrects skew of sheets using alignment members (Japanese Patent Laid-Open Publication No. 2005-42342). This image forming apparatus is equipped with a sensor for detecting a skew amount of sheets, and correcting the skew of a sheet entering between the alignment members based on the detection results sent from the sensor. When the skew amount of the sheet is not smaller than a predetermined amount, the alignment members for correcting the skew are largely retracted to thereby reduce damage to the sheet caused by collision of the sheet with the alignment members.
In the above-described apparatus, however, since the alignment members are each retracted over a shift distance large enough to avoid the collision, the shift distance over which the alignment members are moved each time becomes large, and hence it takes longer time (alignment time) to perform the correction of skew. As a consequence, there is a fear that it is impossible to complete the alignment before the next conveyed sheet arrives, resulting in jamming of the sheet. On the other hand, if a sufficiently long time period is secured for an interval at which each sheet is conveyed so as to cope with the long alignment time, the productivity of image formation and post-processing is reduced.